import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution10 {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 the head node
     * @return ListNode类
     */
    public ListNode sortInList (ListNode head) {
        // write code here
        if(head == null || head.next == null){
            return head;
        }
        ListNode fast = head.next;
        ListNode slow = head;
        while(fast != null && fast.next != null){
            fast = fast.next.next;
            slow = slow.next;
        }
        fast = slow.next;
        slow.next = null;
        ListNode head1 = sortInList(head);
        ListNode head2 = sortInList(fast);
        return merge(head1, head2);
    }
    public ListNode merge(ListNode head1, ListNode head2){
        if(head1 == null ){
            return head2;
        }
        if(head2 == null){
            return head1;
        }
        ListNode root = new ListNode(0);
        ListNode cur = root;
        while(head1 != null && head2 != null){
            if(head1.val < head2.val){
                cur.next = head1;
                head1 = head1.next;
            } else {
                cur.next = head2;
                head2 = head2.next;
            }
            cur = cur.next;
        }
        if(head1 != null){
            cur.next = head1;
        }
        if(head2 != null){
            cur.next = head2;
        }
        return root.next;
    }
}